As global warming and air pollution become more severe, techniques for suppressing carbon dioxide emission into the atmosphere have been aggressively developed. Particularly, a method of efficiently trapping carbon dioxide emitted from thermoelectric power plants or boiler equipment has been under development.
Among various methods of trapping gas, a chemical absorption method using absorbent liquid has been most suitable to trapping carbon dioxide of large capacity. According to a gas collecting plant using the chemical absorption method, carbon dioxide emitted from thermoelectric power plants or boiler equipment is absorbed in absorbent liquid in an absorption tower and saturated absorbent liquid containing carbon dioxide is heated in a regeneration tower to separate regeneration gas containing the carbon dioxide from the absorbent liquid.
According to the conventional gas collecting plant, the carbon dioxide and the absorbent liquid contact with each other at a rectifier mounted in the absorption tower. The rectifier has an apparatus for collecting the absorbent liquid at a center portion mounted on a filler or a separating plate for separating gas evenly mounted on an upper portion of the absorption tower to prevent the absorbent liquid from mixing with the gas. That is, gas and liquid is prevented from communicating by changing a structure of the upper portion of the absorption tower. However, it is very difficult to control the conventional gas collecting plant when abnormal phenomena occur due to fast linear velocity of gas at a lower portion of the absorption tower and absorbent liquid drop.
In addition, a reboiler for heating the absorbent liquid is mounted at the regeneration tower as energy source for regeneration. The reboiler heats the absorbent liquid for regeneration to separate the gas contained in the absorbent liquid. The gas separated from the absorbent liquid moves toward the upper portion of the regeneration tower to be collected into a condenser, and the remaining gas is discharged from the regeneration tower.
Conventionally, a kettle reboiler or a thermocyphon reboiler is used.
The kettle reboiler includes first and second parts therein divided by a wall. A heater or a heat-exchanger is disposed in the first part, and an absorbent liquid outlet is formed at the second part. If the absorbent liquid containing gas is supplied to an upper portion of the reboiler, a level of the absorbent liquid in the reboiler rises. The absorbent liquid is heated by the heater or the heat-exchanger, and the gas is separated from the absorbent liquid and moves upwardly. As the absorbent liquid is supplied continuously, the absorbent liquid from which the gas is removed or which contains less gas crosses the wall and moves to the second part. After that, the absorbent liquid is discharged from the reboiler through the absorbent liquid outlet. According to the kettle reboiler, slosh occurs due to liquid wave generated by liquid drop and boiling of mixed liquid. Therefore, it is difficult to control a level of the absorbent liquid precisely.
The thermocyphon reboiler includes a heater or a heat-exchanger therein, and an absorbent liquid outlet is formed at a bottom surface of the reboiler. If the absorbent liquid containing the gas is supplied to an upper portion of the reboiler, the absorbent liquid in the reboiler is heated by the heater or the heat-exchanger and the gas is separated from the absorbent liquid and moves upwardly. At this time, the absorbent liquid from which the gas is removed or which contains less gas moves toward the bottom surface of the reboiler and is discharged from the reboiler through the absorbent liquid outlet. According to the thermocyphon reboiler, a level of the absorbent liquid is hard to be controlled due to boiling. In addition, since there is no wall in the boiler, the mixed liquid remains in the reboiler in a very short time. Therefore, less energy is supplied to the mixed liquid and gas separation efficiency for regeneration is very low.
In addition, a supply path of the mixed liquid and a discharge path of the gas separated from the mixed liquid are the same in the kettle reboiler and the thermocyphon reboiler. Therefore, if bubbles occur due to heating, the mixed liquid cannot reach the heater or the heat-exchanger due to the bubbles. If this condition continues, the level of the mixed liquid in the regeneration tower is raised too high that the absorption tower and the regeneration tower cannot work.
Furthermore, a gas collecting plant using the chemical absorption method includes a condenser for condensing the regeneration gas and generating condensate. A reflux apparatus discharges gas evaporated from the condensate to an exterior thereof to collect the gas and supplies the condensate back into the regeneration tower.
According to a conventional gas collecting plant, the condenser and the reflux apparatus are separately disposed in order to control a level of the condensate in the reflux apparatus. As a result, a volume of the gas collecting plant becomes large, and a large space is necessary to mount the gas collecting plant. In addition, since the reflux apparatus and the condenser are separated, a large amount of heat loss occurs between the reflux apparatus and the condenser.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.